Method and device for truing grinding wheel, and grinding device

ABSTRACT

In a grinding machine comprising conductive grinding wheels, the invention presents a truing technique capable of truing grindstone surfaces of grinding wheels at high precision in a short time.  
     For example, in the case of truing flat annular grindstone surfaces ( 10   a,    10   a ) of a pair of mutually opposite grinding wheels ( 1, 2 ) simultaneously, an electro-discharge truing electrode ( 20 ) is disposed oppositely between the grindstone surfaces ( 10   a,    10   a ) of the two grinding wheels ( 1, 2 ), and while traversing relatively parallel along the both grindstone surfaces ( 10   a,    10   a ), the grindstone surfaces ( 10   a,    10   a ) are trued without making contact by the electro-discharge action between the electro-discharge truing electrode ( 20 ) and both grindstone surfaces ( 10   a,    10   a ).

TECHNICAL FIELD

[0001] The present invention relates to a truing method for grindingwheel, its truing device and grinding machine, and more particularly toan electro-discharge truing technology for truing the grinding wheel bymaking use of electro-discharge action in a grinding machine comprisingthe grinding wheel composed of conductive grindstone such as metal bonddiamond grindstone.

BACKGROUND ART

[0002] Recently, as one of the latest precision machining techniques,the grinding technique using super-abrasive grains is highly noticed,and the diamond grindstone having diamond abrasive grains bound by resinor metal binding material is preferably used as an ideal grindstone forgrinding rigid and brittle materials such as ceramics.

[0003] In the grinding machine using such super-abrasive grains as thegrinding wheel, the grinding wheel was conventionally trued in thefollowing manner.

[0004] For example, in the case of a vertical double disk surfacegrinding machine using metal bond diamond grinding wheel, its truingmethod is as shown in FIG. 14(a), in which a dressing stone b for truingis inserted between rotating grinding wheels a, a, and the bond (bindingmaterial) B of the grindstone surface in the grinding wheels a, a isshaved off by the abrasive grains released from the dressing stone b,and the grinding wheel is trued while dressing the abrasive grains A ofthe grindstone.

[0005] That is, the grinding wheel of super-abrasive grains of thesurface grinding machine was trued by shaving off the bond B by usingthe released abrasive grains from the dressing stone b as the tool,which is known as the lapping technique.

[0006] The conventional truing method by such lapping method had thefollowing problems, and its improvement has been demanded.

[0007] That is, in truing of grinding wheel by lapping technique, sincethe grinding wheel is trued by the lapping action of released abrasivegrains, sharpness of abrasive grains deteriorates. It also took a longtime when truing the grinding wheel by the lapping technique.

[0008] In particular, in truing the grinding wheel of double disksurface grinding machine, as shown in FIG. 14(b), if the balance ofpressure applied to the dressing stone b is broken by the grindingwheels a, a in the truing process, the arm c supporting the dressingstone b is deflected, and accurate truing of grinding wheels a, a isdifficult, and truing of high precision is not expected.

[0009] The invention is devised in the light of such problems in theprior art, and it is hence an object thereof to present a truingtechnique capable of truing the grinding wheel in a short time and at ahigh precision, in a grinding machine comprising a conductive grindingwheel, and a grinding machine operating on such grinding technique.

DISCLOSURE OF THE INVENTION

[0010] To achieve the object, the truing method for grinding wheel ofthe invention is a method of truing the grinding wheel in a grindingmachine for grinding a work by a grinding wheel driven by rotation, andmore specifically the grinding wheel is composed of a conductivegrindstone having abrasive grains bound by a conductive bindingmaterial, and an electro-discharge truing electrode disposed oppositelyto the grindstone surfaces of the conductive grinding wheel is traversedrelatively along the grindstone surfaces of the grinding wheel, and thegrindstone surfaces of the grinding wheel are trued by theelectro-discharge action.

[0011] In a preferred embodiment, the gap dimension between thegrindstone of the grinding wheel and electro-discharge truing electrodeis controlled according to an electrical information of theelectro-discharge position. The electrical information of theelectro-discharge position is either the current flowing in the currentfeed circuit or the electro-discharge voltage at the electro-dischargeposition, and it is particularly suited to a case of truing a pair ofgrinding wheels disposed oppositely in the double disk surface grindingmachine simultaneously by single truing means.

[0012] The truing device of grinding wheel of the invention is a deviceprovided in a grinding machine for grinding a work by rotating grindingwheels, for truing the grinding wheel having abrasive grains bound by aconductive binding material, and it comprises an electro-dischargetruing electrode disposed oppositely to the grindstone surfaces of thegrinding wheel, current feeding means for feeding current to thegrinding wheel and electro-discharge truing electrode, and truingelectrode driving means for traversing the electro-discharge truingelectrode parallel along the grindstone surfaces of the grinding wheel.

[0013] In a preferred embodiment, the electro-discharge truing electrodeis a disk-shaped rotary electrode which is driven by rotation. In thiscase, the rotary electrode is preferred to have coolant supply means forinjecting a coolant at its side, and air supply means for injecting airtoward the gap between the grindstone of the grinding wheel and rotaryelectrode.

[0014] The grinding machine of the invention is a grinding machine forgrinding a work by grinding wheels driven by rotation, and comprisesgrinding wheels composed of grindstones having abrasive grains bound bya conductive binding material, grinding wheel rotary driving means forrotating and driving the grinding wheels, grinding wheel infeed drivingmeans for moving the grinding wheels in the infeed direction,electro-discharge truing means for truing the grinding wheels byelectro-discharge action, and control means for controlling the grindingwheel rotary driving means, grinding wheel infeed driving means, andelectro-discharge truing means synchronously with each other, and theelectro-discharge truing means includes an electro-discharge truingelectrode disposed oppositely to the grindstones of the grinding wheel,current feeding means for feeding current to the grinding wheel andelectro-discharge truing electrode, and truing electrode driving meansfor traversing the electro-discharge truing electrode parallel along thegrindstone surfaces of the grinding wheel.

[0015] In a preferred embodiment, the control means controls thegrinding wheel rotary driving means, grinding wheel infeed drivingmeans, and electro-discharge truing means synchronously with each other,so as to true the grinding wheel by electro-discharge action whiletraversing the electro-discharge truing electrode relatively along thegrindstone surfaces of the grinding wheel.

[0016] The grinding wheels are cup wheels having a flat annulargrindstone surface, and a pair of cup wheels are disposed oppositely toeach other to construct a double disk surface grinding machine, and theboth cup wheels are trued simultaneously by the single electro-dischargetruing means. In this case, the control means controls the grindingwheel infeed driving means so as to adjust the gap dimension between thegrindstone of the grinding wheel and electro-discharge truing electrodeaccording to the result of detection from the current detecting meansfor detecting the current flowing in the current feeding circuit of thecurrent feeding means.

[0017] When the invention is applied in a double disk surface grindingmachine comprising a pair of opposite grinding wheels, for truing themutually opposite cup wheels having a flat annular grindstone at thesame time, the electro-discharge truing electrode is disposed oppositelybetween the annular grindstone surfaces of the two grinding wheels, andis relatively traversed parallel along the both annular grindstonesurfaces of the two grinding wheels, so that the both annular grindstonesurfaces of the two grinding wheels are trued by electro-dischargewithout making contact by the electro-discharge action between theelectro-discharge truing electrode and both grinding wheels. As aresult, the grinding wheels can be trued in a short time withoutspoiling the edge of abrasive grains of the grindstones.

[0018] Gap control, that is, the control of the gap dimension betweenthe grindstone surfaces of the grinding wheels and the electro-dischargetruing electrode is executed according to the electrical information ofthe electro-discharge position, and in the double disk surface grindingmachine, in particular, the current flowing in the current feedingcircuit of each grindstone of the grinding wheel or theelectro-discharge voltage at the electro-discharge position is used asthe electrical information of the electro-discharge position. Therefore,when truing the pair of grinding wheels disposed oppositely by onetruing means simultaneously, gap control of high precision is realizedbetween the grindstone surfaces of the grinding wheels and theelectro-discharge truing electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a perspective view of a partial block diagram showing aschematic configuration of truing device of conductive grinding wheel ofa vertical double disk surface grinding machine in a preferredembodiment of the invention.

[0020]FIG. 2 is a side view of truing electrode drive unit in the truingdevice.

[0021]FIG. 3 is a plan view of the truing electrode drive unit.

[0022]FIG. 4 is a schematic plan view showing traversing operation ofelectro-discharge truing electrode in the truing device, in which FIG.4(a) shows an oscillating traversing operation of electro-dischargetruing electrode by the electro-discharge truing electrode drive unit,and FIG. 4(b) shows a backward traversing operation of electro-dischargetruing electrode by other electro-discharge truing electrode drive unit.

[0023]FIG. 5 is a block diagram of configuration of gap control systemof electro-discharge truing in the grinding machine.

[0024]FIG. 6 is a flowchart showing the control process in the gapcontrol system.

[0025]FIG. 7 is a diagram explaining the principle of gap control ofupper and lower grinding wheels in the gap control system, in which FIG.7(a) is a schematic structural diagram showing the system, and FIG. 7(b)is a diagram showing a current characteristic flowing in each currentfeeding circuit of upper and lower grinding wheels in this system.

[0026]FIG. 8 is a diagram explaining the principle of gap control ofupper and lower grinding wheels in other gap control system making useof supply voltage, in which FIG. 8(a) is a schematic structural diagramshowing the system, and FIG. 8(b) is a diagram showing the relationbetween a supply voltage characteristic and a current characteristicflowing in each current feeding circuit of upper and lower grindingwheels in this system.

[0027]FIG. 9 is a diagram explaining the electro-discharge truing methodof grinding wheel in the electro-discharge truing device, in which FIG.9(a) is a model diagram showing the principle of electro-dischargetruing in the double disk surface grinding machine, and FIG. 9(b) is aschematic sectional view showing a state of arm member of theelectro-discharge truing electrode drive unit at the time of truing.

[0028]FIG. 10(a) to (c) are model diagrams showing time course changesof each process in the truing operation.

[0029]FIG. 11 shows other example of application of electro-dischargetruing of the invention, in which FIG. 11(a) shows a case of applicationin horizontal double disk surface grinding machine, and FIG. 11(b) showsa case of application in vertical single disk surface grinding machine.

[0030]FIG. 12 is a schematic side sectional view showing other exampleof grindstone of grinding wheel truing by other electro-discharge truingby the vertical double disk surface grinding machine.

[0031]FIG. 13 is a schematic perspective view showing a case ofapplication of electro-discharge truing of the invention in a centerlessgrinding machine.

[0032]FIG. 14 is an explanatory diagram for explaining a truing methodby using a dressing stone in a conventional vertical double disk surfacegrinding machine, in which FIG. 14(a) is a magnified view of grindstoneof grinding wheel at the time of truing, and FIG. 14(b) shows an armmember for supporting the dressing stone at the time of truing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Preferred embodiments of the invention are described in detailbelow while referring to the accompanying drawings.

[0034]FIG. 1 through FIG. 13 show grinding machines according to theinvention, and same reference numerals refer to same constituent membersor elements throughout the drawings.

[0035] A grinding machine having a truing device according to preferredembodiments is shown in FIG. 1 to FIG. 10. This grinding machine 1 isspecifically a vertical double disk surface grinding machine having apair of grinding wheels 2, 3 disposed oppositely up and down coaxially,and mainly comprises the pair of grinding wheels 2, 3, grinding wheelrotary drive devices (grinding wheel rotary driving means) 4, 5,grinding wheel infeed drive devices (grinding wheel infeed drivingmeans) 6, 7, an electro-discharge truing device (electro-dischargetruing means) 8, and a control device (controlling means) 9.

[0036] The pair of grinding wheels 2, 3 are cup wheels of identicalstructure, and the end portion is a grindstone 10 having abrasive grainsbound by a conductive binding material, and its end plane 10 a is a flatannular grindstone surface.

[0037] The supporting structure of these grinding wheels 2, 3 is notspecifically shown but is a known basic structure, and they aredetachably mounted on the leading ends of rotary spindles 15, 16disposed coaxially, and the grindstone surfaces 10 a, 10 a are disposedto be parallel to each other and opposite vertically.

[0038] The rotary spindles 15, 16 are rotatably supported on wheel headsof a device platform not shown, and are respectively coupled to thegrinding wheel drive devices 4, 5 through a power transmissionmechanism.

[0039] The grinding wheel drive devices 4, 5 are for rotating anddriving the upper and lower grinding wheels 2, 3, and incorporate rotarydrive sources such as motors (not shown).

[0040] The wheel heads for rotating and supporting the grinding wheels2, 3 are elevatable in the vertical direction by means of a slidedevice, and are coupled respectively to the grinding wheel infeed drivedevices 6, 7.

[0041] The grinding wheel infeed drive devices 6, 7 are for moving theupper and lower grinding wheels 2, 3 in the infeed direction (verticaldirection in the shown example), and comprise feed mechanism (not shown)such as ball screw mechanism and infeed drive source (not shown) such asmotor.

[0042] The both grinding wheels 2, 3 are composed of conductivegrindstones 10 of which end portion has abrasive grains bound by aconductive binding material. Specifically, in these grinding wheels 2,3, the grindstones 10 are integrally disposed in the end portions of thegrinding wheel main bodies 2 a, 3 a made of conductive material.

[0043] The grindstones 10 are made of abrasive materials A, specificallysuper-abrasive grains such as fine diamond abrasive grains and CBN(cubic boron nitride) abrasive grains, and these abrasive grains A, A, .. . are bound by a conductive binding material B. The conductive bindingmaterial B is preferably conductive metal bond, conductive resin bondcontaining conductive substance, or the like (properties of abrasivegrains A and binding material B are shown in FIG. 9 (a)).

[0044] These grinding wheels 2, 3 are electrically connected to the (+)pole of a direct-current power supply device 12 through a currentfeeding wire 11 a. Specifically, as shown in FIG. 1, brush-like currentfeeders 13 a, 13 b are disposed at the leading ends of the currentfeeding wire 11 a, and these current feeders 13 a, 13 b sliderespectively on rotary spindles 15, 16 of the grinding wheels 2, 3, andare connected electrically.

[0045] In this configuration, through these rotary spindles 15, 16,direct-current power source can be supplied from the singledirect-current power supply device 12 into the upper and lower grindingwheels 2, 3 (specifically grindstones 10), and the upper and lowergrinding wheels 2, 3 are rotary electrodes of the (+) pole.

[0046] The electro-discharge truing device 8 is for truing thegrindstones 10, 10 of the upper and lower grinding wheels 2, 3 byelectro-discharge action, and mainly comprises an electro-dischargetruing electrode 20, a current feed device (current feeding means) 21,and truing electrode drive device (truing electrode driving means) 22.

[0047] The electro-discharge truing electrode 20 is an electrode forelectro-discharge truing of grindstone surfaces 10 a, 10 a of the upperand lower grinding wheels 2, 3, and is specifically a rotary electrodeof a small narrow disk, and is disposed oppositely to the bothgrindstone surfaces 10 a, 10 a.

[0048] That is, the cylindrical outer circumference 20 a of theelectro-discharge truing electrode 20 is a cylindrical electrode surfaceopposite to the grindstone surfaces 10 a, 10 a of the grinding wheels 2,3 forming the other rotary electrode, and the electro-discharge truingelectrode 20 is designed to traverse parallel along the both grindstonesurfaces 10 a, 10 a by means of truing electrode drive device 22 asexplained below.

[0049] Further, the electro-discharge truing electrode 20 iselectrically connected to the (−) pole of the direct-current powersupply device 12 through the current feeding wire 11 b, and is used asthe electro-discharge truing electrode of the (−) pole.

[0050] The current feed device 21 is for feeding current to thegrindstones 10, 10 of the grinding wheels 2, 3 and electro-dischargetruing electrode 20, and mainly comprises an upper current feedingcircuit 21 a for the upper grinding wheel 2, a lower current feedingcircuit 21 b for the lower grinding wheel 3, and the direct-currentpower supply device 12 for supplying power source to these currentfeeding circuits 21 a, 21 b.

[0051] The upper current feeding circuit 21 a forms a closed circuit ofdirect-current power source device 12, electro-discharge truingelectrode 20, upper grinding wheel 2, and back to direct-current powersupply device 12, and the lower current feeding circuit 21 b forms aclosed circuit of direct-current power source device 12,electro-discharge truing electrode 20, lower grinding wheel 3, and backto direct-current power supply device 12. These current feeding circuits21 a, 21 b are provided with current detecting sensors 25 a, 25 b fordetecting the current flowing in the circuits, and detection currentsIa, Ib of these current detecting sensors 25 a, 25 b are sent to thecontrol device 9 respectively as mentioned below, thereby functioning ascontrol factors for controlling and adjusting the gap dimension betweenthe grindstone surface 10 a and electro-discharge truing electrode 20.

[0052] The truing electrode drive device 22 is a device for traversingthe electro-discharge truing electrode 20 parallel along the grindstonesurface 10 a of the grindstone 10 as shown in FIG. 4(a), and itspecifically has a structure as shown in FIG. 2 and FIG. 3, and theelectro-discharge truing electrode is traversed in a range including theoutermost peripheral edge 10 b and innermost peripheral edge 10 c of theannular grindstone surface 10 a.

[0053] The truing electrode drive device 22 mainly comprises, as shownin FIG. 2, a platform 30, an oscillating table 31 oscillatably disposedon the platform 30 by way of an oscillating mechanism not shown, and anarm member 32 fixed on the oscillating table 31.

[0054] At the leading end of the arm member 32, a rotary shaft 33 of theelectro-discharge truing electrode 20 is rotatably supported throughbearings 34, 34, and the rotary shaft 33 is linked to an electroderotary drive device 36 through a power transmission mechanism 35described below, so that the electro-discharge truing electrode 20 canbe driven by rotation.

[0055] The electrode rotary drive device 36 specifically has a motor 37fixed on the oscillating table 31, and a drive shaft 38 is linked to therotary shaft (not shown) of the motor 37. The drive shaft 38 rotatablysupported at the base end side of the arm member 32 through bearings 39,39. The drive shaft 38 and rotary shaft 33 of the electro-dischargetruing electrode 20 are mutually linked by way of the power transmissionmechanism 35. The power transmission mechanism 35 is composed oftransmission pulleys 35 a, 35 b fixed on both shafts 33, 38, and atransmission belt 35 c for linking these transmission pulleys 35 a, 35b.

[0056] At one end of the rotary shaft 33, a current feeder 37 isprovided for connecting to the (−) electrode of the direct-current powersupply device 12, and a voltage of (−) can be applied to theelectro-discharge truing electrode 20. Accordingly, as the bearing 34 ofthe rotary shaft 33, preferably, a ceramic bearing is used from theviewpoint of prevention of current leak.

[0057] Moreover, the truing electrode drive device 22 also incorporatesa coolant supply device (coolant supplying means) 40 for injectingcoolant for cooling the electro-discharge truing electrode 20 at thetime of electro-discharge truing operation described below, and an airsupply device (air supplying means) 41 as coolant removing device forinjecting air for removing the coolant deposits from theelectro-discharge truing electrode 20.

[0058] The coolant supply device 40 includes a coolant supply source notshown, a coolant injection port 40 a disposed oppositely to the innerside of the electro-discharge truing electrode 20 at the leading end ofthe arm member 32, and a piping 40 b for coolant supply connecting them.A pressurized coolant supplied from the coolant supply source isinjected to the inner side of the electro-discharge truing electrode 20from the coolant injection port 40 a by way of the piping 40 b.

[0059] The air supply device 41 is for removing the coolant blown to theelectro-discharge truing electrode 20 by air injection, and it isspecifically composed of an air supply source not shown, an airinjection nozzle 41 a disposed oppositely to the cylindrical electrodesurface 20 a of the electro-discharge truing nozzle 20 at the leadingend of the arm member 32, and a piping 41 b for air injection supply forconnecting them. A pressurized air supplied from the air supply sourceis injected to the cylindrical electrode surface 20 a of theelectro-discharge truing electrode 20 from the leading end of the airinjection nozzle 41 a through the piping 41 b, and the coolant depositsare removed from the cylindrical electrode surface 20 a.

[0060] By removing the coolant blown to the electro-discharge truingelectrode 20 by the coolant supply device 40, an electrical insulationis assured between the cylindrical electrode surface 20 a of theelectro-discharge truing electrode 20 and the annular grindstone surface10 a of the grindstone 10.

[0061] In this preferred embodiment, since the grinding machine 1 is avertical double disk surface grinding machine, the number of airinjection nozzles 41 a corresponds to the number of grinding wheels 2,3, and hence a pair of upper and lower nozzles are disposed at the sideof the arm member 32 as shown in FIG. 2. Besides, since the airinjection nozzle 41 a is provided in order to assure an electricalinsulation between the electro-discharge truing electrode 20 andgrindstone 10, it is installed so that the air injection direction ofthe nozzle leading end can be adjusted so as to inject the air into thegap of them (see double dot chain line in FIG. 2). Further, the leadingend of the air injection nozzle 41 a is disposed slightly eccentric tothe outside from the center of the cylindrical electrode surface 20 a asshown in FIG. 3 so as not to disturb blowing of the coolant injectedfrom the coolant injection port 40 a to the inner side of theelectro-discharge truing electrode 20.

[0062] The control device 9 is a control center for controlling theoperation of the components of the surface grinding machine 1, and isspecifically composed of a microcomputer storing specified controlprograms.

[0063] That is, this control device 9 controls the operation of thegrinding wheel rotary drive devices 4, 5 and grinding wheel infeed drivedevices 6,7 of the grinding wheels 2, 3, current feeding device 21 ofelectro-discharge truing device 8, truing electrode drive device 22, andelectrode rotary drive device 36 mutually and synchronously, and ishence capable of controlling the revolutions (rotating speed) and infeedof grinding wheels 2, 3, the traverse move (moving direction and movingspeed) of the electro-discharge truing electrode 20, application ofvoltage to the electro-discharge truing electrode 20, and pressurizingoperation of the coolant supply source and air supply source, in mutualrelationship.

[0064] In the surface grinding machine 1 having such configuration, whentruing the grinding wheels 2, 3, the control device 9 controls thegrinding wheels 2, 3 and electro-discharge truing electrode 20 asfollows, so that on-machine electro-discharge truing of grinding wheel 2is realized.

[0065] A. Principle and Basic Operation of Electro-Discharge Truing

[0066] Upon start of electro-discharge truing, the control device 9 setsthe gap of the upper and lower grinding wheels 2, 3 and the rotatingspeed of the grinding wheel 2, 3 as specified, and rotates and drivesthe electro-discharge truing electrode 20 at specified speed.

[0067] Parallel to these processes, the control device 9 turns on thepower source of the direct-current power supply device 12, and applies aspecified voltage to the grinding wheels 2, 3 and electro-dischargetruing electrode 20.

[0068] Upon completion of these processes, the control device 9 operatesthe oscillating mechanism of the oscillating table 31, and traverses theelectro-discharge truing electrode 20 from the outermost peripheral edge10 b side of the annular grindstone surface 10 a to the innermostperipheral edge 10 c side (see FIG. 4(a)).

[0069] At this time, a voltage of (+) is applied to the grindstonesurfaces 10 a, 10 a of the grinding wheels 2, 3, and a voltage of (−) isapplied to the electro-discharge truing electrode 20, and hence as theelectro-discharge truing electrode 20 advances, an electro-dischargeaction occurs between the both electrodes, and thereby, as shown in FIG.9(a), the metal bond B portion of the grindstone 10 is melted andremoved, and an annular grindstone surface 10 a is newly formed.

[0070] In the illustrated preferred embodiment, the coolant injectedfrom the coolant injection port 40 a of the coolant supply device 40 isatomized by the air injection from the air injection nozzle 41 a of theair supply device 41, and the mist exists between the annular grindstonesurface 10 a and electro-discharge truing electrode 20, therebyincreasing the electro-discharge effect.

[0071] The forming process of the annular grindstone surface 10 a bythis electro-discharge action is explained more specifically byreferring to FIG. 10, and first the electro-discharge truing electrode20 is traversed from the outermost peripheral edge 10 b of the annulargrindstone surface 10 a to the innermost peripheral edge 10 c, and themetal bond B is melted and removed from the surface of the annulargrindstone surface 10 a (see FIG. 10(a)).

[0072] By this traversing motion, when the electro-discharge truingelectrode 20 reaches the innermost peripheral edge 10 c of the annulargrindstone surface 10 a (see FIG. 10(b)), this time, an infeed action isapplied to the grinding wheels 2, 3 and the electro-discharge truingelectrode 20 is traversed again toward the outermost peripheral edge 10b (see FIG. 10(c)).

[0073] The traversing motion of the electro-discharge truing electrode20 and infeed operation of the grinding wheels 2, 3 are repeatedsequentially until the annular grindstone surface 10 a is formed in aspecified shape.

[0074] Thus, in the double disk surface grinding machine 1 of thepreferred embodiment, in truing operation of the grinding wheels 2, 3since the annular grindstone surface 10 a is trued without makingcontact by the electro-discharge truing technique, the grinding wheelscan be trued in a short time without spoiling the edge of abrasivegrains of the grindstones, and also in truing operation of double disksurface grinding machine, high precision truing is realized withoutdeflection of arm member 32 as shown in FIG. 9(b).

[0075] B. Speed Control of Traversing Motion

[0076] In the surface grinding machine 1 of the preferred embodiment asdescribed above, in truing operation of grinding wheels 2, 3 whiletraversing the electro-discharge truing electrode 20 parallel along theannular grindstone surface 10 a of the grinding wheels 2, 3, if therotating speed of the grinding wheels 2, 3 is kept at a specific speed,only by traversing the electro-discharge truing electrode 20 at aspecific speed, uniform truing is not realized because of difference inthe peripheral speed in the inner and outer peripheral position of theannular grindstone surface 10 a.

[0077] Therefore, in the surface grinding machine 1 of the preferredembodiment, the control device 9 controls the traversing speed asfollows so that the peripheral speed of the annular grindstone surface10 a may be almost constant all the time against the electro-dischargetruing electrode 20 during the traversing operation.

[0078] That is, in the preferred embodiment, since the traversing motionof the electro-discharge truing electrode 20 is realized by the rotarydrive of the oscillating mechanism, the control device 9 controls toadjust the rotating speed of the oscillating mechanism, in synchronismwith the traversing motion of the electro-discharge truing electrode 20,so as to slow down the traversing speed when the electro-dischargetruing electrode 20 is positioned near the outer periphery of theannular grindstone surface 10 a, or accelerate when located near theinner periphery of the annular grindstone surface 10 a, thereby keepingconstant the removal amount per unit area of the annular grindstonesurface 10 a opposite to the electro-discharge truing electrode 20.

[0079] When controlling the traversing speed, the rotating speed of theoscillating mechanism is kept constant, and the rotating speed of thegrinding wheel 2 may be adjusted in synchronism with the traversingmotion of the electro-discharge truing electrode 20.

[0080] In short, the control device 9 controls and adjusts at leasteither one of the traversing speed of electro-discharge truing electrode20 by the truing electrode drive device 22 or rotating speed of grindingwheels 2, 3 by the grinding wheel rotary drive devices 4, 5, andcontrols so that the peripheral speed of the annular grindstone surfacemay be constant against the electro-discharge truing electrode 20 in thetraversing motion.

[0081] Thus, in the preferred embodiment, since the traversing speed ofthe electro-discharge truing electrode 20 or the rotating speed of thegrinding wheels 2, 3 are controlled so as to keep constant the removalamount per unit area of the annular grindstone surfaces 10 a, 10 bopposite to the electro-discharge truing electrode 20 during traversingmotion, the entire surface of the annular grindstone surfaces 10 a, 10 amay be trued uniformly.

[0082] Concerning the control of traversing speed, if the grindingwheels 2, 3 to be trued are deformed and the annular grindstone surfaces10 a, 10 a are not flat, repeated traversing motions are needed toeliminate the undulations completely by control of the traversing speedonly, and hence it is preferred to correct the control of traversingspeed as follows by the control device 9.

[0083] That is, in this case, the direct-current power supply device 12is provided with electro-discharge voltage detecting means (not shown)for detecting the electro-discharge voltage in electro-discharge truingoperation, the electro-discharge voltage is detected, and the traversingspeed is corrected according this electro-discharge voltage.

[0084] More specifically, when the grindstone surface 10 a projects, theelectro-discharge voltage is lower, and when the grindstone surface 10 asinks, the electro-discharge voltage is higher, and by detecting theelectro-discharge voltage by the voltage detection sensor not shown, theresult of detection is sent to the control device 9.

[0085] According to the result of detection, the control device 9 slowsdown the traversing speed when the grindstone surface 10 a projects, andintensively removes the projecting portion of the metal bond B, or whenthe grindstone surface 10 a sinks, the traversing speed is acceleratedto decrease the removal amount of the metal bond B.

[0086] In order words, by correcting the traversing speed depending onundulations of the grindstone surfaces 10 a, 10 a, the number ofrepetitions of traversing motion of the electro-discharge truingelectrode 20 can be decreased, so that truing may be realized in a shorttime.

[0087] C. Gap Control

[0088] To perform such electro-discharge truing of high precision, it isrequired to maintain a preset dimension of gap between the grindstonesurfaces 10 a, 10 a of the grinding wheels 2, 3 and theelectro-discharge truing electrode 20, and in this preferred embodimentthe control device 9 is designed to control the grinding wheel infeeddrive devices 6, 7 according to the electrical information of theelectro-discharge position.

[0089] A configuration of the gap control system is shown in FIG. 5, andin the illustrated preferred embodiment, as the electrical informationof the electro-discharge position, the current flowing in the currentfeeding circuits 21 a, 21 b is utilized. Although not shown in thedrawing, the electro-discharge voltage at the electro-discharge positiondetected by a voltage detection sensor (not shown) may be also used asthe electrical information of the electro-discharge position.

[0090] That is, in the gap control system shown in FIG. 5, the currentsIa, Ib flowing in the current feeding circuits 21 a, 21 b are detectedby current detection sensors 25 a, 25 b, and the detected currents Ia,Ib are sent into current waveform shaping units 50 a, 50 b for removingnoise and supplied into the control device 9. In the control device 9,comparators 51 a, 51 b compare the detected currents Ia, Ib with presetvalue, and send the result of comparison to arithmetic units 52 a, 52 b.The arithmetic units 52 a, 52 b calculate correction amounts necessaryfor the grinding wheels 2, 3 from the result of comparison (the infeednecessary for obtaining the optimum gap (target value)), and thecorrection amounts are adjusted to equalize the gap of the both upperand lower grinding wheels 2, 3, and corresponding control signals aresent to the grinding wheel infeed drive devices 6, 7 of the upper andlower grinding wheels 2, 3.

[0091] In the preferred embodiment, the set value is determined in twostages, and set value 1 is the upper limit (for example, 10A) ofallowable current of the gap necessary for electro-discharge truing, andset value 2 is the lower limit (for example, 8A).

[0092] In this gap control system, the gap of the upper and lowergrinding wheels 2, 3 is controlled as follows (see flowchart in FIG. 6).

[0093] In the basic motion (traversing motion) of electro-dischargetruing mentioned above, when the electro-discharge truing electrode 20moves to the traverse position capable of discharging between thegrindstone surfaces 10 a, 10 a of the grinding wheels 2, 3, anelectro-discharge start signal is fed, and electro-discharge truing ofthe upper and lower grinding wheels 2, 3 is started at the same time.

[0094] During electro-discharge truing operation, the currents Ia, Ibflowing in the current feeding circuits 21 a, 21 b are always detectedby the current detection sensors 25 a, 25 b, and the detected currentsIa, Ib are compared with set values 1, 2 by the comparators 51 a, 51 b,and depending on the result of comparison, the arithmetic units 52 a, 52b calculate and adjust the necessary correction values.

[0095] When the electro-discharge truing electrode 20 moves to atraverse position incapable of discharging between the grindstonesurfaces 10 a, 10 a of the grinding wheels 2, 3, an electro-dischargeend signal is fed, and electro-discharge truing of the upper and lowergrinding wheels 2, 3 is stopped at the same time, and control signalscorresponding to the result of calculation are sent from the arithmeticunits 52 a, 52 b to the grinding wheel infeed drive devices 6, 7 of theupper and lower grinding wheels 2, 3.

[0096] As a result, the grinding wheel infeed drive devices 6, 7 movethe grinding wheels 2, 3 by the required infeed amount according to thecontrol signals, and the gap between the grinding wheels 2, 3 isadjusted to the target value.

[0097] Specifically, (i) when the maximum detection current duringtraversing, that is, the maximum value of the currents Ia, Ib detectedduring traversing is larger than the set value 1, a backward signal issent as control signal to the grinding wheel infeed drive devices 6, 7,and upon completion of traversing motion, the grinding wheels 2, 3 aremoved back (returned) by a preset amount (for example, 2 μm). Or, (ii)when the maximum detected currents Ia, Ib during traversing are smallerthan the set value 1 but larger than the set value 2, an OK signal issent as control signal to the grinding wheel infeed drive devices 6, 7,and upon completion of traversing motion, the grinding wheels 2, 3 aremoved forward (infeed) by a preset amount (for example, 1 μm (wornportion of grindstone)) (ordinary infeed). Further, (iii) when themaximum detected currents Ia, Ib during traversing are smaller than theset value 2, a forward signal is sent as control signal to the grindingwheel infeed drive devices 6, 7, and upon completion of traversingmotion, the grinding wheels 2, 3 are moved forward (infeed) by a presetamount (for example, 4 μm) (air cut correction). In the gap controlsystem of the preferred embodiment, as the electrical information of theelectro-discharge position, the currents flowing in the upper and lowercurrent feeding circuits 21 a, 21 b are utilized owing to the followingreason.

[0098] That is, as shown in FIG. 8, in the case of electro-dischargetruing of one side only, for example, the upper grinding wheel 2, itsgap is controlled by maintaining the voltage determined by the voltage Vdeclining in inverse proportion to the current I as shown in FIG. 8(b).

[0099] In such gap control system, when the both upper and lowergrinding wheels 2, 3 are trued at the same time, for example, if the gapbetween the electro-discharge truing electrode 20 and upper grindingwheel 2 is large and the gap to the lower grinding wheel 3 is small, thecurrent amount of the upper current feeding circuit 21 a is small andthe current amount of the lower current feeding circuit 21 b is large,but the change of supply voltage that can be detected by the voltagedetection sensor (not shown) in the direct-current power supply device12 is the change of voltage V due to combined current of the uppercurrent feeding circuit 21 a and lower current feeding circuit 21 b, andwhen the gap of the grinding wheels 2, 3 cannot be controlled.

[0100] Accordingly, in the preferred embodiment, by employing the systemshown in FIG. 7 as mentioned above, by the electro-discharge truingdevice 8 having one direct-current power supply device 12, if thegrindstone surfaces 10 a, 10 a of the upper and lower grinding wheels 2,3 are trued at a time, the gap can be controlled in both grinding wheels2, 3. Although not shown specifically, if the electro-discharge voltageof the electro-discharge position is utilized as the electricalinformation of the electro-discharge position, the gap can be similarlycontrolled as mentioned above.

[0101] Thus, in the preferred embodiment, by controlling the gap of thegrinding wheels 2, 3 by using the currents flowing in the currentfeeding circuits 21 a, 21 b of the grindstone surfaces 10 a, 10 a, whenthe pair of mutually opposite grinding wheels 2, 3 are trued at the sametime by the single electro-discharge truing device 8, the gap can becontrolled at high precision between the grindstone surfaces 10 a, 10 aof the grinding wheels 2, 3.

[0102] The preferred embodiment shows a preferred embodiment of theinvention, but the invention is not limited to this preferred embodimentalone, but the design can be changed or modified within the scope, andexamples are given below.

[0103] (1) In the illustrated preferred embodiment, the invention isapplied in the vertical double disk surface grinding machine, but it canbe also applied in a horizontal double disk surface grinding machine asshown in FIG. 11(a), or not limited to the double disk surface grindingmachine, it can be also applied in a single disk surface grindingmachine as shown in FIG. 11 (b). In other words, the invention can beapplied in surface grinding machines of any type as far aselectro-discharge truing is executed by traversing the electro-dischargetruing electrode 20 relatively along the annular grindstone surface 10 aof the surface grinding machine 1.

[0104] In this case, in the single disk surface grinding machine in FIG.11(b), as the electrical information of electro-discharge position forgap control of the grindstone surface 10 a by the control device 8, asexplained in FIG. 8, the supply voltage detected by the voltagedetection sensor in the direct-current power supply device 12 can beutilized.

[0105] (2) In the illustrated preferred embodiment, a rotary electrodedriven by rotation is shown as the electro-discharge truing electrode20, but the electro-discharge truing electrode may be also realized bythe fixed electrode not driven by rotation.

[0106] (3) In the illustrated preferred embodiment, when traversing theelectro-discharge truing electrode 20, the structure for oscillating thearm member 32 is used, but as shown in FIG. 4(b), for example, it may bealso realized by a structure of electrode forward and backward movingmechanism for moving the electro-discharge truing electrode 20 forwardor backward parallel to the grindstone surface 10 a by moving in or outthe arm member 32.

[0107] (4) In the illustrated preferred embodiment, when traversing theelectro-discharge truing electrode 20, sliding motion of theelectro-discharge truing electrode 20 is shown, but theelectro-discharge truing may be also executed by sliding the grindingwheel 2.

[0108] (5) In the illustrated preferred embodiment, the annulargrindstone surfaces 10 a of the grinding wheels 2, 3 are flat, but atruing profile as shown in FIG. 12, for example, is also possible bychanging the infeed of the grinding wheel 2 in synchronism with thetraversing motion of the electro-discharge truing electrode 20.

[0109] (6) The invention may be also applied in a centerless grindingmachine as shown in FIG. 13, and in this case, same as in the case ofthe single head surface grinding machine in FIG. 11(b), as theelectrical information of electro-discharge position for gap control bythe control device 8 of the cylindrical grindstone surface 10 a in acylindrical grinding wheel 102, the supply voltage detected by thevoltage detection sensor in the direct-current power supply device 12can be utilized as explained in FIG. 8.

[0110] In FIG. 13, reference numeral 103 shows an adjusting wheel, and104 is a blade for supporting a work W.

[0111] (7) Further the invention may be applied, although not shown, invarious other grinding machines such as cylindrical grinding machine andinter (internal grinding) reciprocating surface grinding machine.

INDUSTRIAL APPLICABILITY

[0112] As described herein, according to the invention, when truing theconductive grinding wheels, since electro-discharge truing is executedwhile traversing the position of the electro-discharge truing electroderelatively to the grindstone surface of grinding wheel of the grindingmachine, the required time for truing is substantially shortened ascompare with the truing operation by the conventional lapping technique.

[0113] Moreover, since the electro-discharge truing electrode andannular grindstone surface do not contact with each other in truingoperation, the edges of the abrasive grains of the grindstone are notworn, and sharpness of abrasive grains remains unchanged, so that truingof high precision is realized. In particular, in truing of double diskgrinding machine, distortion due to deflection of the conventional armis eliminated, and truing of higher precision is possible, and twogrinding wheels can be trued at a time by one truing operation, and theworking time is shortened notably.

[0114] Further, the gap control of the dimension between the grindstonesurface of the grinding wheel and the electro-discharge truing electrodecan be done by making use of the electrical information of theelectro-discharge position, and in the double disk surface grindingmachine, in particular, since the currents flowing in the currentfeeding circuits of the grindstone surface are utilized as theelectrical information of the electro-discharge position, when truing apair of mutually opposite grinding wheels simultaneously by one truingmeans, gap control of high precision is possible between the grindstonesurfaces of grinding wheels and the electro-discharge truing electrode.

1. A truing method for grinding wheel, being a method of truinggrindstones of grinding wheels in a grinding machine for grinding a workby grinding wheels driven by rotation, wherein said grinding wheel iscomposed of a conductive grindstone having abrasive grains bound by aconductive binding material, an electro-discharge truing electrodedisposed oppositely to the grindstone surfaces of the conductivegrindstones is traversed relatively along the grindstone surfaces, andthe grindstone surfaces are trued by electro-discharge action, and thegap dimension between the grindstone surfaces of grinding wheel andelectro-discharge truing electrode is controlled according to anelectrical information of the electro-discharge position.
 2. The truingmethod for grinding wheel of claim 1, wherein the gap dimension betweenthe grindstone surfaces of grinding wheel and electro-discharge truingelectrode is controlled according to the electrical information of theelectro-discharge position detected during traversing motion uponcompletion of traversing motion of the electro-discharge truingelectrode.
 3. The truing method for grinding wheel of claim 2, whereinthe electrical information of the electro-discharge position is thecurrent flowing in the current feeding circuit.
 4. The truing method forgrinding wheel of claim 2, wherein the electrical information of theelectro-discharge position is the electro-discharge voltage of theelectro-discharge position.
 5. The truing method for grinding wheel ofclaim 1, wherein said grinding wheel has a flat annular grindstonesurface, and the electro-discharge truing electrode is traversed alongthe annular grindstone surface in a range including the outermostperipheral edge and innermost peripheral edge of the annular grindstonesurface.
 6. The truing method for grinding wheel of claim 5, wherein itis controlled to keep constant the peripheral speed of the annulargrindstone surfaces opposite to the electro-discharge truing electrodeduring traversing motion, by adjusting at least either the traversingspeed of the electro-discharge truing electrode or the rotating speed ofthe grinding wheel.
 7. The truing method for grinding wheel of claim 1,wherein said grinding wheel has a cylindrical grindstone surface, andthe electro-discharge truing electrode is traversed parallel along thecylindrical grindstone surface in a range including both ends in theaxial direction of the cylindrical grindstone surface.
 8. A truingdevice of grinding wheel, being a device provided in a grinding machinefor grinding a work by rotating grinding wheels, for truing the grindingwheel having abrasive grains bound by a conductive binding material ofthe grinding wheels, comprising: an electro-discharge truing electrodedisposed oppositely to the grindstone surfaces, current feeding meansfor feeding current to the grindstones and electro-discharge truingelectrode, and truing electrode driving means for traversing theelectro-discharge truing electrode parallel -along the grindstonesurfaces of the grinding wheels.
 9. The truing device of grinding wheelof claim 8, wherein said electro-discharge truing electrode is adisk-shaped rotary electrode which is driven by rotation.
 10. The truingdevice of grinding wheel of claim 9, further comprising: coolant supplymeans for injecting a coolant provided at the side said rotaryelectrode, and air supply means for injecting air toward the gap betweenthe grindstone surface and rotary electrode.
 11. The truing device ofgrinding wheel of claim 8, wherein said truing electrode driving meanshas an oscillating mechanism for oscillating the electro-dischargetruing electrode parallel along the annular grindstone surface.
 12. Thetruing device of grinding wheel of claim 8, wherein said truingelectrode driving means has an electrode forward and backward movingmechanism for moving the electro-discharge truing electrode back andforth parallel along the grindstone surface.
 13. A grinding machine,being a grinding machine for grinding a work by grinding wheels drivenby rotation, comprising: grinding wheels composed of grindstones havingabrasive grains bound by a conductive binding material, grinding wheelrotary driving means for rotating and driving the grinding wheels,grinding wheel infeed driving means for moving the grinding wheels inthe infeed direction, electro-discharge truing means for truing thegrindstones of the grinding wheels by electro-discharge action, andcontrol means for controlling the grinding wheel rotary driving means,grinding wheel infeed driving means, and electro-discharge truing meanssynchronously with each other, wherein said electro-discharge truingmeans includes an electro-discharge truing electrode disposed oppositelyto the grinding wheels, current feeding means for feeding current to thegrindstone surfaces and electro-discharge truing electrode, and truingelectrode driving means for traversing the electro-discharge truingelectrode parallel along the grindstone surfaces, and said control meanscontrols the gap dimension between the grindstone surfaces of thegrinding wheels and the electro-discharge truing electrode according tothe electrical information of the electro-discharge position detectedduring traversing upon completion of traversing motion of theelectro-discharge truing electrode.
 14. The grinding machine of claim13, wherein said control means controls the grinding wheel rotarydriving means, grinding wheel infeed driving means, andelectro-discharge truing means synchronously with each other, so as totrue the grindstone surfaces of grinding wheel by electro-dischargeaction while traversing the electro-discharge truing electroderelatively along the grindstone surfaces.
 15. The grinding machine ofclaim 13, wherein said electrical information detecting means is acurrent detection sensor for detecting the current flowing in thecurrent feeding circuit.
 16. The grinding machine of claim 13, whereinsaid electrical information detecting means is a voltage detectionsensor for detecting the electro-discharge voltage at theelectro-discharge position.
 17. The grinding machine of claim 13,wherein said grinding wheels are cup wheels having a flat annulargrindstone surface, and a pair of cup wheels are disposed oppositely toeach other to construct a double disk surface grinding machine, and thegrindstone surfaces of the both cup wheels are trued simultaneously bythe single electro-discharge truing means.
 18. The grinding machine ofclaim 13, wherein said grinding wheels are cup wheels having a flatannular grindstone surface, and said control means controls to keepconstant the peripheral speed of the annular grindstone surfacesopposite to the electro-discharge truing electrode during traversingmotion, by adjusting at least either the traversing speed of theelectro-discharge truing electrode by the truing electrode driving meansor the rotating speed of the grinding wheel by the grinding wheel rotarydriving means.